A preliminary investigation of the ferric leaching of a pyrite/arsenopyrite flotation concentrate

Although considerable work on the leaching of pyrite using Fe(III) is reported in the literature, to date very little work on the chemical leaching of arsenopyrite, using Fe(lll) has been reported Batch, ferric leaching experiments, each 48 hours in length, wc!re carried out in sealed, baffled, agitated vessels. Varying quantities of Fe(III), ranging from 0 to 0.54 M were added to a slurry, containing 10 g.l(-1) concentrate. The redox potential was monitored continuously. Samples were taken at regular intervals and the total iron and arsenic concentration of the supernatant was determined The results showed that no leaching occurred in the absence of Fe(III). However, considerable leaching of arsenic occurred in the reactors to which Fe(III) was added Furthermore the results suggest that the chemical leaching rate may be a function of the redox potential, and not of the absolute Fe(III) concentration. The stoichiometry determined for the ferric leaching of arsenopyrite agreed with the stoichiometry postulated by previous researchers [1], viz: FeAsS + 5Fe(3+) --> S-0 + As3+ + 6Fe(2+) Furthermore, the results obtained are consistent with the hypothesis that the leaching of arsenopyrite, the oxidation of As(III) to As(V), the leaching of pyrite, and the precipitation of ferric arsenate compete for the available Fe(III). (C) 1997 Elsevier Science Ltd.